This application claims the priority of Korean Patent Application No. 2003-5928, filed on Jan. 29, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a field emission device, a field emission display adopting the same, and a manufacturing method thereof.
2. Description of the Related Art
A field emission device is a structure in which a cathode where an electron emission source is formed so as to emit electrons on a substrate, and a gate electron for inducing field emission are formed in an array. While electrons are emitted from an internal electron emission source of the field emission device, arcing occurs in an internal vacuum space between a cathode plate on which an electron emission source is provided and an anode plate having a phosphor screen where electrons are collided with one another. It is estimated that arcing occurs by discharge occurring when avalanche phenomena of a large amount of gases is instantaneously generated due to outgassing. Also, arcing often occurs even when chamber testing of a field emission array (FEA) formed on a cathode plate is performed or even when an anode voltage of 1 kV or more is applied to a combination of the cathode plate and an anode plate so as to perform testing of a field emission device. If surveying of the surface of the FEA in which arcing occurred is performed using an optical microscope, a damage caused by arcing is mainly observed in a gate edge of a gate hole. It is estimated this is because due to the pointed gate edge of the gate hole, arcing easily occurs under a high electric field. Arcing causes electrical short circuit between an anode to which an anode voltage having the highest electric potential is applied and a gate electrode to which a gate voltage relatively lower than the anode voltage is applied. Thus, the anode voltage is directly applied to the gate electrode, and a gate oxide used to electrically insulates the cathode electrode and the gate electrode and a resistive layer formed on the cathode electrode are damaged by this high voltage. This possibility more often occurs as the anode voltage increases. Consequently, arching possibility further increases when the anode voltage increases over 1 kV for the device having a simple structure in which the cathode plate and the anode plate are isolated by a spacer, and thus, it is difficult to achieve a high luminance field emission device that stably operates at a high voltage.
Meanwhile, such a conventional field emission device has a structure in which electrons are extracted by one gate electrode from the cathode and are simply accelerated toward a phosphor screen, and thus, emitted electron beams are collided with a phosphor deviating from a given pixel. This problem may be solved by an additional electrode for controlling electron beams emitted on the aforementioned electron beam path, for example, an additional electrode for focusing electron beams at a target position on a phosphor layer. This electrode corresponds to an additional grid electrode in the field emission device and is generally formed as a single body, unlike in a first gate electrode provided in a strip shape. The grid electrode of this single body serves to control electron beams as described above and prevent arcing which may occur in the aforementioned field emission device.
Korean Patent Application No. 2000-7115 and U.S. patent application Ser. No. 5,710,483 disclose a field emission device adopting a grid electrode as described previously.
A field emission device disclosed in U.S. Pat. No. 5,710,483 has a structure in which a grid electrode is formed by depositing a metallic material, whereas a field emission device disclosed in Korean Patent Application No. 2000-7115 has a structure in which an additional metallic mesh is suspended by a spacer between an anode plate and a cathode plate and the anode plate and the cathode plate are separated from each other.
As disclosed in U.S. Pat. No. 5,710,483, the size of the grid electrode formed by depositing the metallic material is limited by the size of deposition equipment. This limitation in the size of deposition equipment causes to limit the size of the field emission device which can be manufactured, and thus, it is not proper to manufacture a large-sized field emission device. Thus, an apparatus for deposing a metallic layer required to manufacture a large-sized field emission device must to be newly designed and manufactured, but vast costs are required. Meanwhile, the thickness of the grid electrode formed by the metallic deposition layer is limited to maximum 1.5 microns, and thus is not enough to effectively control electron beams.
In the field emission device disclosed in Korean Patent Application No. 2000-7115, a grid electrode (mesh grid) is made of a metallic plate. Thus, the size of the grid electrode is not limited as described above, and its thickness can be freely selected, and electron beams can be effectively controlled.
FIG. 1 is a cross-sectional view schematically illustrating an example of a conventional field emission device adopting a mesh grid. Referring to FIG. 1, a cathode plate 10 and an anode plate 20 are spaced apart from each other by a spacer 30. A space between the cathode plate 10 and the anode plate 20 is vacuumized. Thus, due to an internal negative pressure, the cathode plate 10 and the anode plate 20 are securely coupled to each other in the state that the spacer 30 is placed therebetween.
On the cathode plate 10, a cathode electrode 12 is formed on a rear plate 11, and a gate insulating layer 13 is formed on the cathode electrode 12. A through hole 13a is formed in the gate insulating layer 13, and the cathode electrode 12 is exposed to the bottom of the through hole 13a. An electron emission source 14 such as carbon nanotube (CNT) is formed on the cathode electrode 12 exposed through the through hole 13a. A gate electrode 15 having a gate hole 15a corresponding to the through hole 13a is formed on the gate insulating layer 13.
Meanwhile, on the anode plate 20, an anode electrode 22 is formed inside of a front plate 21, a phosphor layer 23 on the anode electrode 22 is formed opposite to the gate hole 15a, and a black matrix 24 is formed in the other portion of the anode electrode 22.
A mesh grid 40 is interposed between the cathode plate 10 and the anode plate 20 having the above structure. The mesh grid 40 is supported by the spacer 30 in the state that the mesh grid 40 is spaced apart from the cathode plate 10 and the anode plate 20 by a predetermined gap.
The mesh grid 40 has a fixing hole 41 through which the spacer 30 passes and an electron beam-controlling hole 42 which corresponds to the gate hole 15a. A binder 43 is filled in the fixing hole 41 so that the mesh grid 40 is coupled to the spacer 30.
A method for coupling a spacer in a conventional field emission device having the above structure will be described as below.
First, the spacer 30 is disposed in the anode plate 20 at a predetermined interval in the state that the phosphor layer 23 is not plactized. Next, the spacer 39, fixed in the anode plate 20, is inserted in the fixing hole 41 of the mesh grid 40 manufactured by extracting from a metallic plate, and then, the binder 43 for fixing the spacer 30 is filled in the fixing hole 41.
The mesh grid 40 and the spacer 30 are aligned, the binder 43 is cured, and then, the phosphor layer 23 is fired. The anode plate 20 and the cathode plate 10 are aligned with each other, and vacuum packaging is performed.
In the aforementioned conventional method, when a binder is cured at a temperature of about 120° C. and a phosphor layer is fired at a temperature of about 420° C., a mesh grid may be deformed and may be not well aligned with an anode plate. In particular, during vacuum packaging, secondary deformation of the mesh grid and scattering of alignment of the mesh grid with the anode plate occur at a process temperature of about 300° C. or more. Also, the mesh grid is separated from the cathode plate. Thus, as shown in FIG. 2, electrons emitted from one electron emission source do not pass through a corresponding hole of the mesh grid but stray electrons pass through another adjacent hole through a gap between the mesh grid and the cathode plate. The stray electrons are collided with another phosphor layer, and thus, color purity of an image may be lowered.
Due to the deformation and scattering of the mesh grid and generation of the stray electros, which may cause lowering of picture quality, the performance of the field emission device is deteriorated and thus, a new method for solving these problems is required.